State laws cannot trump federal law. Did whoever you talk to offer to tell you exactly WHAT state law is "overriding" the federal law? I would ask them to provide the exact state law which they are referencing and then I would turn around and provide it to NHTSA, specifically the OVSC (202) 366-3151.
What you can do is get the email address of the people at your local DMV and copy
importandcertification@dot.gov in an email asking for clarification on federal regulations for a box 1 import to be allowed in Hawaii. Specifically, mention you are wanting to register said vehicle and the DMV is giving you problems (then explain the issues).
The problem is that Hawaii, like a few other states, carries redundant laws to re-cite federal law for registration requirements. This practice is incorrect as they did not account for older and foreign vehicles which are legal to be imported to the US, thus the issue is created that "said vehicle does not conform to FMVSS and therefore we will not register it". NHSTA takes a stance that title and registration is state's responsibility and not a federal matter, however in the case where the state simply does not understand federal law there's room to argue this until you're blue in the face and get a title. In fact, most states have laws to protect residents and give them the right to a title if the vehicle is legal, which in the case of a box 1 import - it is. If at this point you are still not getting anywhere then I recommend seeking a Hawaii based lawyer that specializes in working with the DMV and auto dealers, they will be well versed in title and registration issues with the state and likely have a field day with this. All you have to do is kick up a little dust and people at the DMV will start to move with a purpose.
Last year I had personally called the DMV in Hawaii and asked about registering a JDM vehicle in the state and was told there was no issue as long as there was paperwork to support the purchase of the vehicle and it was legally imported.